[lkml]   [2009]   [Mar]   [21]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
    SubjectRe: [RFC][PATCH 3/3] perf_counter: new output ABI - part 1
    On Sat, 2009-03-21 at 20:45 +1100, Paul Mackerras wrote:
    > Ingo Molnar writes:
    > > i think it would still be nice to allow plain old-fashioned
    > > poll()+read() loops ... but the logistics of that seem difficult.
    > > mmap() seems to fit this better - and it's probably faster as well.
    > > (as we have to construct the kernel-space pages anyway, so mapping
    > > them isnt that big of an issue)
    > >
    > > per-CPU-ness will be handled naturally via per-cpu counters.
    > >
    > > Paul, can you see any hole/quirkiness in this scheme?
    > The one thing I can see that we would lose is the ability to have a
    > signal delivered on every event. The PAPI developers want to be able
    > to get a signal generated every time the counter overflows, and
    > previously we could do that using the O_ASYNC flag, but now we'll only
    > get a signal every page's worth of events.

    Ah, nice, didn't know about O_ASYNC and was thinking we should perhaps
    provide some signal too, seems that's already taken care of, sweet :-)

    > So I think we want userspace to be able to say how often we should
    > generate a poll event, i.e. provide a way for userspace to say "please
    > generate a poll event every N counter events". That would also solve
    > the problem of 1 page not being a valid configuration - you could set
    > the poll interval to the number of events that fit in half a page, for
    > instance.

    Sure, can do, sounds like s sensible extension -- except it will be hard
    to guess the event size for some future events like callchains and mmap

     \ /
      Last update: 2009-03-21 11:33    [W:0.023 / U:0.332 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site